Field of the Invention
The invention relates to a light emitting diode (LED) and a manufacturing method thereof, and particularly relates to a micro LED (μLED) and a manufacturing method thereof.
Description of Related Art
Along with evolution of lighting technology, conventional incandescent bulbs and fluorescent lamps are gradually replaced by micro light emitting diodes (μLEDs) due to low luminous efficiency or environmental protection. The μLED has advantages of long service life, compact volume, high luminous efficiency and low power consumption, etc., so that it is widely used in various different applications.
In recent years, a technique of reducing the size of the conventional LED to micron scale is developed, and the size-reduced LED is referred to as a micro LED (μLED). When the μLEDs are used in the field of the display technique, each of the μLEDs may be taken as a sub-pixel in a display panel, and such display panel is referred to as a micro LED display panel. The μLED of each sub-pixel of the micro LED display panel may be controlled via addressing and individually driven to emit light, and has advantages of high brightness, low power consumption, high resolution, high color saturation, etc. Compared to an organic light emitting diode (OLED) display, the micro LED display panel further has an advantage of a long service life. Therefore, the micro LED display panel is regarded as a mainstream technique in the next generation for display.
However, a manufacturing process of the μLED often encounters following problems. For example, for a common flip-chip μLED, since two electrodes are respectively disposed on a mesa portion and a recess portion with different horizontal heights, when the μLED is bonded to an external substrate, it often causes a tilt phenomenon of the μLED and leads to a poor bonding yield. Moreover, since the size of the μLED is small relative to a conventional LED, the above-mentioned tilt phenomenon of the μLED is more severe. In order to resolve the tilt phenomenon, one solution is to dispose the two electrodes on two mesa portions with the same horizontal height, such that the surfaces of the two electrodes are devised to stand on the same horizontal plane. However, since such solution requires to etch a hole in the mesa configured for an N-type electrode, and form a protective layer on the surface of the hole to electrically isolate a P-type doped semiconductor layer and a light emitting layer from the mesa portion of the N-type electrode, and then etch a part of the protective layer to expose an underneath N-type doped semiconductor layer, so as to electrically connect the N-type electrode and the N-type doped semiconductor layer. However, since the hole is very tiny (below 10 μm×10 μm), the protective layer is hard to be formed in the hole, which makes the manufacturing process of the μLED become more difficult. Moreover, the existence of the protective layer also limits the size of the N-type electrode. Therefore, a yield of the μLED manufactured based on the existing manufacturing process is low, which limits the development of the μLED technology.